Preparation of cotton fabrics for dyeing



FIP8309 3,353,903 PREPARATION OF COTTGN FABRKCS FOR DYEING Howard L. Potter and Neil J. Stalter, Wilmington, DeL,

assignors to E. I. du Pont de Nemours and Company,

Wilmington, Del., a corporation of Delaware No Drawing. Filed Feb. 28, 1966, Ser. No. 530,387

6 Claims. (till. 8-111) This application is a continuation-in-part of our pending application Ser. No. 498,092, filed Oct. 19, 1965, now abandoned.

This invention relates to the preparation of fabrics for dyeing. More particularly it relates to a method for rapidly preparing greige woven cotton fabrics for dyeing, which method can be practiced employing well-known and generally available equipment.

Woven cotton fabrics in the greige state contain fatty, waxy, resinous and mote impurities which render them non-absorbent and contribute to the relatively dark color of the fibers. They also contain the sizing agent, generally starch, employed during weaving. All such materials must be essentially completely removed and the fabric must be whitened substantially in any successful method of preparing the fabric for subsequent dyeing.

The widely used prior methods for converting greige fabric into an absorbent, relatively white state suitable for dyeing have generally involved separate desizing, scouring and bleaching treatments, usually requiring the use of large J-boxes capable of storing several thousands of pounds of fabric during treating periods of about one hour or longer. Efforts have been made to reduce the treating times and to eliminate the need for large J-boxes and the creasing and fabric abrasion problems attending their use, but most such efforts have not resulted in commercially accepted methods. An exception is the bleaching method described in Potter and Terhune US. Patent 2,960,383 wherein treating times of 2 to 10 minutes are employed. Because of the relatively short treating times, the storage treatments of the Potter and Terhune method can be effectively accomplished in small J -boxes, thereby considerably reducing the creasing problem because of the relatively small weight of fabric piled in the J-box. Although this method has met with considerable commercial success, it has not entirely eliminated the problem of creasing and rub marks, and its practice, in most instances, entails treating periods of 8 to 10 minutes, which are still too long to eliminate entirely the need for using J-box storage facilities.

This invention provides a method for rapidly preparing woven cotton fabrics for dyeing, which method can be practiced using well-known and commonly available equipment other than Lboxes. All types of woven cotton fabrics can be rapidly converted by the method of the invention into fabrics possessing the absorbency, cleanliness and whiteness required for dyeing to any desired shade.

In accordance with the method of the invention, a woven cotton fabric, generally in the greige state, i.e., the undesized and unscoured state, is subjected in its open width and extended state sequentially to at least the first two of the following treatment stages:

STAGE 1 The fabric is dampened or impregnated with an aqueous solution containing 6 to 13%, preferably 8 to 11%, caustic soda or caustic potash. Although not essential, the solution will advantageously also contain 0.2 to 2%, preferably 0.4 to 0.7% of a water-soluble molecularly dehydrated phosphate and/or also a wetting agent. The dampened fabric is subjected to the direct action of satu- 3,353,903 Patented Nov. 21, 1967 rated steam at about atmospheric pressure for a time of from about 1 to 2 minutes, then rinsed with water.

STAGE 2 The fabric from Stage 1 is impregnated or dampened with an aqueous solution containing: (a) 1 to 5% caustic soda or caustic potash, preferably 1 to 3% when two stages are to be used and 2 to 4% when three stages are to be used; (b) 0.2 to 2.5%, preferably 0.3 to 1.5% hydrogen peroxide (H 0 and (c) a peroxide stabilizer at a concentration effective to prevent excessive decomposition of the hydrogen peroxide. Advantageously, although not essential, the solution will also contain a wetting agent and/or an organic heavy metal sequestering agent. The dampened fabric is subjected to the direct action of saturated steam at about atmospheric pressure for a time of from about 1 to 2 minutes, then rinsed with water.

STAGE 3 If a further treatment stage is needed or desired, the fabric from Stage 2 is impregnated or dampened with an aqueous solution containing (a) 0.8 to 3%, preferably 1 to 2%, caustic soda or caustic potash; (b) 0.2 to 2.5%, preferably 0.7 to 1.6%, H 0 and (c) a peroxide stabilizer at a concentration elfective to prevent excessive decomposition of the hydrogen peroxide. A wetting agent and/or an organic heavy metal sequestering agent may also be present. The fabric dampened with the treating solution is then subjected to the direct action of saturated steam at about atmospheric pressure for from about 1 to 2 minutes, then finally Washed.

It has been found that many woven greige cotton fabrics can be rapidly and satisfactorily conditioned for dyeing by being subjected sequentially to the treatments of only Stages 1 and 2 above. However, in some instances, a subsequent treatment in accordance with the above Stage 3 may be indicated, particularly when a whiteness somewhat higher than that obtained by the two-stage treatment is found to be desirable. Whether practicing either the two-stage or the three-stage embodiment of the invention, the fabric is handled throughout in its open width and extended condition, so that no storage of the fabric in piled .or bulk form is involved and the problem of creasing and rub marks is entirely eliminated. In each stage, a continuous length of the fabric in open width and extended state is dampened with the treating solution for that stage, the dampened fabric is passed through a steamer in which an atmosphere of saturated steam at substantially atmospheric pressure is continuously maintained, and the steamed fabric is then rinsed. The fabric is continuously advanced in open width through all stages to be employed, and the rate of advancement will be such as to provide a residence time in the steamer of each stage of about 1 to 2 minutes.

The seaming treatment for 1 to 2 minutes in each stage is conveniently effected by passing the fabric through a conventional steamer of the type commonly employed as steamers or aging boxes in dyeing establishments. Such a steamer generally comprises an enclosed rectangular box or steam chamber having entry and exit ports (generally narrow slots) for the open width fabric, upper and lower horizontally spaced parallel rows of rolls within the steam chamber over which the fabric is drawn to form a series of loops, means such as draw rolls for drawing the fabric through the steamer, and means for supplying steam to the interior of the steam chamber so as to maintain therein a substantially air-free atmosphere of saturated steam at substantially atmospheric pressure, whereby the fabric in the steamer will be heated to and maintained at the temperature of the steam, e.g., 205 to about 212 F., for the 1 to 2 minute period during which the fabric is in the steamer. The general design of such a steamer or aging box is well-known and is described in many patents, e.g., Rupp US. Patent 1,913,615.

The method of the invention produces excellent results, even when applied to heavy (at least 2 yds./ 1b.), tightly woven fabrics, such as twills, poplins, 'sateens, drills and jeans, in the greige (undesized and unscoured) state. The conversion of such fabrics to a state suitable for dyeing has been generally regarded as a formidable task and its accomplishment by prior methods has generally required long storage periods in J-boxes, with attending disadvantages. Although highly effective with such difficult-to-process fabrics, generally even when using the twostage embodiment of the invention, the method of the invention can also be employed in preparing for dyeing lighter and less tightly woven fabrics and also fabrics which have been desized or prescoured. However, it is generally preferred not to employ separate desizing or prescouring treatments in view of the excellent results obtained with greige fabrics. The method, in both its twoand three-stage embodiments, has been successfully applied to a wide variety of all-cotton fabrics and blended cotton fabrics, e.g., cotton-nylon and cotton-polyester blends, all in the greige state.

In each of the two or three stages employed, the fabric is impregnated or dampened with an amount of the treating solution equal to from about 80 to 150%, preferably 90 to 110%, of the dry weight of the fabric. This is conveniently accomplished by immersing the fabric in the solution, then expressing, e.g., by means of squeeze rolls, excess solution from the fabric.

Stabilizers for alkaline peroxide solutions are Wellknown and at least one such stabilizer should be present in the solutions for Stages 2 and 3 at a concentration effective to prevent excessive decomposition of the hydrogen peroxide. The water-soluble salts of mole-cularly dehydrated phosphoric acid (i.e., the water-soluble molecularly dehydrated phosphates) are particularly effective stabilizers for that purpose. Examples thereof are sodium and potassium pyrophosphates, sodium hexametaphosphate and sodium tripolyphosphate. Such phosphate will generally be used at concentrations of 0.2 to 2%; the preferred concentrations are 0.4 to 0.7%. Sodium silicate, e.g., the 42 B. solution (approximate composition: Na O, 25% SiO and 65% H O) commonly employed in peroxide bleach solutions, is also a highly effective stabilizer for the solutions of Stages 2 and 3. Effective concentrations thereof are 0.5 to 3% and the preferred concentrations are 1 to 2%. Other silicate stabilizers and also organic phosphate stabilizers may also be used in either or both such solutions, as may also combinations of stabilizers, for example, sodium silicate with a phosphate and sodium silicate with sodium pyrophosphate and a soluble magnesium salt such as magnesium sulfate.

The wetting agents which may be advantageously used in the solutions for all stages are conventional anionic and nonionic detergents, such as the common soluble soaps and the synthetic detergents such as the sodium and potassium alkyl sulfates, the sodium and potassium alkyl and alkylbenzene sulfonates, ethylene oxide condensates and alkoxylate aryl polyether alcohols. The concentrations thereof in the treating solution will generally range from 0.1 to 1%, preferably 0.2 to 0.5%. Organic heavy metal sequestering agents may at times be advantageously employed in the treating solutions of Stages 2 and 3, e.g., at concentrations of 0.05 to 0.5%, preferably 0.1 to 0.2%. Such agents are polycarboxyamine compounds such as ethylenediamine tetraacetic acid, diethylenetriaminepentaacetic acid, nitrilotriacetic acid and the hydroxyalkyl ethylenediamine triacetic acids, and their sodium salts.

The effective conversion of heavy, tightly woven greige cotton fabrics to a state suitable for dyeing by the present method in the very short steaming periods of not more than about 2 minutes is quite surprising. Such results appear to be due directly to the combined effects of the two or three stages constituting the present method and to the specific compositions of the treating solutions employed therein. The first stage, in which an unusually high concentration of caustic soda is used, initiates and advances the desizing and scouring reactions sufficiently so that the preparation can be completed in the subsequent short stage or stages. The second stage effects the removal of most of the impurities, including the size and motes, due to the oxidative-extractive action of the treating solution. The caustic soda content of the treating solution of the second stage is unusually high compared with prior peroxide-containing solutions employed commercially for high temperature fabric treatments. Although such a high caustic soda content in a peroxide solution is usually regarded as damaging to the fabric when the solution is employed under high temperature conditions, it has been found that little, if any, damage to the fabric results from the present use of such solutions because of the very short steaming times which characterize the present method. Furthermore, the first and second stage treatments, carried out in sequence, effect surprisingly rapid and satisfactory purification of the fabric for most dyeing operations. The third stage is primarily an oxidative stage which further increases the whiteness of the fabric and essentially completes removal of the small amounts of impurities remaining after the second stage. In many instances the full white and exceptional purification achieved by the third stage treatment are not required and entirely satisfactory preparation of the fabric for dyeing will result without using any third stage treatment. However, it may be desirable in some instances to practice all three stages, and it is noteworthy that, when doing so, the over-all amount of caustic soda to which the fabric is subjected in the three stages is much higher than had been regarded as tolerable in prior methods, which higher amount is usable successfully because of the very short times employed. It is the identities and concentrations of the reagents in the treating solutions used that make possible the effective purification of the fabric in such short times.

The invention is illustrated by the following examples. In the examples and elsewhere herein, all reagent concentrations expressed as percentages are by weight.

Example 1 In Stage 1, a 1.8 yd./lb. greige cotton twill fabric was immersed in an aqueous solution containing 10% caustic soda, 0.5% sodium pyrophosphate (Na P O -10H O) and 0.2% sodium lauryl sulfate. The temperature of the solution was F. Excess solution was expressed from the fabric so as to leave it dampened with an amount of the solution equal to the fabric weight. The dampened fabric was heated in an atmosphere of saturated steam at atmospheric pressure (the temperature being approximately 212 F.) for 2 minutes, then rinsed with water. In Stage 2, the fabric was dampened, steamed, then rinsed as previously, except that the treating solution used was one containing 2% caustic soda, 0.5% sodium pyrophosphate, 0.2% sodium lauryl sulfate, 1% sodium silicate (commercial 42 B. solution) and 0.35% H 0 In Stage 3, the dampening, steaming and rinsing operations were again repeated, but this time employing as the treating solution one containing 1% caustic soda, 2% sodium silicate, 0.1% sodium salt of diethylenetriaminepentaacetic acid, 0.1% sodium lauryl sulfate and 1.4% H 0 The above three-stage treatment gave a prepared fabric having a whiteness of 83.0%, as measured by the Hunter Reflectometer, and an absorbency of 0.5 second, as determined by the standard AATCC drop test. It was substantially free of motes and in excellent condition for dyemg.

Example 2 The procedure of Example 1 was repeated except that the steaming period in each stage was only one minute and the solution employed in Stage 3 contained 2.1% H instead of 1.4%. The prepared fabric was essentially free of motes and had a whiteness of 80.9% and an absorbency of 0.6 second.

Example 3 The procedure of Example 1 was repeated except that the solution used in the second stage contained 3% caustic soda instead of 2%. The prepared fabric was essentially free of motes and had a whiteness of 85.2% and an absorbency of 0.4 second.

Example 4 The procedure of Example 1 was repeated except that sodium silicate was omitted from the solutions used in Stages 2 and 3. The prepared fabric was substantially free of motes and had a whiteness of 82.4% and an absorbency of 0.3 second.

Example 5 Example 6 When a 1.8 yd./lb. twill fabric containing 35% cotton and 65% polyester (terephthalic acid-ethylene glycol ester) is processed as described in Example 1, a clean fabric well prepared for dyeing is obtained.

Example 7 The procedure of Example 1 was repeated except that the fabric employed was a heavy (1.1 yd./lb.) greige cotton twill. Despite the heaviness and tight weave of this fabric, the three stage procedure as described in Example 1 gave a prepared fabric having a whiteness of 79.6% and an absorbency of 0.3 second. It was essentially free of motes and in excellent condition for dyeing.

Example 8 A greige coton twill, 1.8 yd./lb., was prepared for dyeing by a two-stage treatment which was a repetition of Stages 1 and 2 of Example 1, except that the treating solution employed in Stage 2 contained 1% caustic soda, 0.7% H 0 1% sodium silicate solution (42 B.), 0.5% sodium pyrophosphate and 0.2% sodium lauryl sulfate. The resulting prepared fabric was essentially mote-free and had a whiteness of 79% and an absorbency of 0.5 second and was satisfactory for dyeing. When the second stage was followed by a third stage using a treating solution containing 1% caustic soda, 0.7% H 0 2% sodium silicate solution, 0.05% Epsom salt, 0.1% sodium lauryl sulfate and 0.1% diethylenetriaminepentaacetic acid (DTPA) with a 2 minute steaming period, the final treated fabric had a whiteness of 84.6% and an absorbency of 0.4 second.

Example 9 A greige cotton twill, 1.8 yd./lb., was prepared for dyeing by a two-stage treatment which was a repetition of Stages 1 and 2 of Example 1, except that the solution for Stage 2 contained 5% caustic soda, 0.35% H 0 1% sodium silicate solution, 0.5% sodium pyrophosphate and 0.2% sodium lauryl sulfate. The treated fabric was essentially mote-free and had a whiteness of 74% and an absorbency of 0.3% and was suitable for dyeing. When the second stage was followed by a third stage as described 6 in Example 8, except that the treating solution therefor contained 1.4% H 0 (instead of 0.35%), the final treated fabric had a whiteness of 85.9% and an absorbency of 0.3 second.

Example 10 A greige cotton twill, 1.8 yd./lb., was prepared for dyeing by a two-stage treatment which was a repetition of Stages 1 and 2 of Example 1, except that the solution for Stage 1 contained 8% (instead of 10%) caustic soda, and the solution for Stage 2 contained 1% (instead of 2%) caustic soda. The treated fabric, which had a whiteness of 76.2% and an absorbency of 0.6 second, was essentially mote-free and satisfactory for dyeing. When the second stage was followed by a third stage as described in Example 8, the final treated fabric had a whiteness of 81.1% and an absorbency of 0.4 second.

Example 11 In a mill trial, about 1400 yards of a greige all-cotton twill, 1 yd./lb., was prepared for dyeing by a continuous two-stage operation in the first stage of which the fabric was saturated with about an equal weight of a solution containing 10.5% caustic soda, 0.5% sodium pyrophosphate and 0.2% of a commercial wetting agent which was an ethylene oxide condensate containing anionic groups. The fabric was drawn continuously in open width from the s'aturator through a steamer containing saturated steam at substantially atmospheric pressure, the retention time in the steamer being 1 minute. Following a continuous rinsing step, the fabric was passed continuously to the sec ond stage in which it was saturated with about an equal weight of treating solution, then drawn continuously through a steamer, the retention time in the steamer being 2 minutes, and then finally rinsed. The fabric was handled throughout in open width. The treating solution for the second stage had a pH of 12 and contained 1.2% caustic soda, 0.8% H 0 2% sodium silicate solution (42 B.), 0.5% sodium pyrophosphate, 0.5% Epsom salt and 0.2% of the wetting agent used in the first stage. The treated fabric had a whiteness of 76.9%, a fluidity value of 1.9 rhes (Guam) and an absorbency of 0.8 second. It was essentially mote-free and in excellent condition for dyeing.

Example 12 The two-stage mill trial of Example 11 was repeated using a greige cotton-nylon twill fabric, 1.13 yd./lb., which fabric was a blend containing cotton and 15% nylon. The treated fabric had a whiteness of 78.9% and an absorbency of 1.6 seconds and was in satisfactory condition for dyeing.

Example 13 The two-stage mill trial of Example 11 was repeated using a greige cotton-polyester twill fabric, 1.3 yd./lb., which fabric was a blend containing equal parts of cotton and a polyester (terephthalic acid-ethylene glycol ester). The treated fabric was essentially mote-free and had a whiteness of 80.7% and an absorbency of 0.8 second. When the procedure was repeated but with a 2 minute steaming period in each stage, the final treated fabric had a whiteness of 84.7% and an absorbency of 0.8 second.

Fabrics prepared according to the above examples have been found to be free of starch as determined by spotting with an iodine solution prepared by adding a small amount of H 0 to a dilute (about 1%) acidic solution of potassium iodide. The prepared fabrics have shown cotton fluidity values of 1.9 to 4.2 rhes (Cuam) which are within the fluidity range for well-prepared fabrics. Such fiuidities indicate that the fabrics are not significantly damaged by the treatment, despite the unusually high concentrations of chemicals in the treating solutions used.

The embodiments of the invention in which an exclusive property or privilege is claimed are as follows:

1. The method of preparing a woven cotton fabric for dyeing comprising subjecting said fabric in open Width and extended state sequentially to at least the first two of the following three treatment stages:

Stage 1- (a) dampening said fabric with an aqueous solution containing 6 to 13% caustic soda or caustic potash;

(b) subjecting the dampened fabric to the direct action of saturated steam at about atmospheric pressure for about 1 to 2 minutes; then (c) rinsing the fabric with water;

Stage 2-- (a) dampening the fabric from Stage 1 with an aqueous solution containing (1) 1 to 5% caustic soda or caustic potash, (2) 0.2 to 2.5% H 0 and (3) a peroxide stabilizer at a concentration effective to prevent excessive decomposition of the H202;

(b) subjecting the dampened fabric to the direct action of saturated steam at about atmospheric pressure for about 1 to 2 minutes; then (c) rinsing the fabric with water;

Stage 3 (a) dampening the fabric from Stage 2 with an aqueous solution containing (1) 0.8 to 3% caustic soda or caustic potash, (2) 0.2 to 2.5% H 0 and (3) a peroxide stabilizer at a concentration effective to prevent excessive decomposition of the H 0 (b) subjecting the dampened fabric to the direct action of saturated steam at about atmospheric pressure for about 1 to 2 minutes; then (c) rinsing the fabric with water.

2. The method of claim 1 wherein the starting fabric is in the greige state and each peroxide-containing solution employed contains sodium silicate as the peroxide stabilizer.

3. The method of claim 1 wherein the starting fabric is in the greige state and each peroxide-containing solution employed contains as the peroxide stabilizer sodium silicate in combination with sodium pyrophosphate and magnesium sulfate.

4. The method of claim 1 wherein the starting fabric is in the greige state and the solutions employed in all stages each contains a water-soluble molecularly dehydrated phosphate.

5. The method of claim 1 wherein the starting fabric is in the greige state and the solutions employed in all stages each contains a wetting agent.

6. The method of claim 1 wherein the starting fabric is in the greige state and the solutions employed in all stages each contains sodium pyrophosphate and a wetting agent, and wherein each peroxide-containing solution employed contains as the peroxide stabilizer sodium silicate in combination with sodium pyrophosphate.

References Cited UNITED STATES PATENTS 2,858,183 10/1958 Potter s 111 2,960,383 11/1960 Potter et al. 8111 3,148,019 9/1964 Gallagher et al. 8-111 LEON D. ROSDOL, Primary Examiner.

M. WEINBLATT, Assistant Examiner. 

1. THE METHOD OF PREPARING A WOVEN COTTON FABRIC FOR DYEING COMPRISING SUBJECTING AID FABRIC IN OPEN WIDTH AND EXTENDED STATE SEQUENTIALLY TO AT LEAST THE FIRST TWOOF THE FOLLOWING THREE TREATMENT STAGES: STAGE 1(A) DAMPENING SAID FABRIC WITH AN AQUEOUS SOLUTION CONTAINING 6 TO 13% CAUSTIC SODA OR CAUSTIC POTASH; (B) SUBJECTING THE DAMPENED FABRIC TO THE DIRECT ACTION OF SATURATED STEAM AT ABOUT ATMOSPHERIC PRESSURE FOR ABOUT 1 TO 2 MINUTES; THEN (C) RINSING THE FABRIC WITH WATER; STAGE 2(A) DAMPENING THE FABRIC FROM STAGE 1 WITH AN AQUEOUS SOLUTION CONTAINNG (1) 1 TO 5% CAUSTIC SODA OR CAUSTIC POTASH, (2) 0.2 TO 2.5% H2O2, AND (3) A PEROXIDE STABILIZER AT A CONCENTRATION EFFECTIVE TO PREVENT EXCESSIVE DECOMPOSITION OF THE H2O2; (B) SUBJECTING THE DAMPENED FABRIC TO THE DIRECT ACTION OF SATAURATED STEAM AT ABOUT ATMOSPHERIC PRESSURE FOR ABOUT 1 TO 2 MINUTES; THEN (C) RINSING THE FABRIC WITH WATER; STAGE 3(A) DAMPENING THE FABRIC FROM STAGE 2 WITH AN AQUEOUS SOLUTION CONTAINING (1) 0.8 TO 3% CAUSTIC SODA OR CAUSTIC POTASH, (2) 0.2 TO 2.5% H2O2, AND (3) A PEROXIDE STABILIZER AT A CONCENTRATION EFFECTIVE TO PREVENT EXCESSIVE DECOMPOSITION OF THE H2O2; (B) SUBJECTING THE DAMPENED FABRIC TO THE DIRECT ACTION OF SATURATED STEAM AT ABOUT ATMOSPHERIC PRESSURE FOR ABOUT 1 TO 2 MINUTES; THEN (C) RINSING THE FABRIC WITH WATER. 